Directly heated oxide cathode

ABSTRACT

A directly heated cathode assembly comprising a tape-shaped member having a perforated central plane portion and end portions longitudinally extending from two sides of the central portion, a cathode plate member in spaced confronting relationship with one surface of the central portion, and electron emissive material embedded within the perforations of the central portion and interposed between the cathode plate member and the central portion. The width of the central portion of the tape-shaped member is greater than that of the end portions. The cathode plate member is secured to the central portion of the tape-shaped member at two oppositely located positions of the central portion spaced from the end portions.

United States Patent Kniper et al.

[451 Sept. 26, 1972 [54] DIRECTLY HEATED OXIDE ATHO1DE [72] Inventors: Adrianus Kuiper; Jan Willem Brouns; Bauke Visser, all of Emmasingel, Eindhoven, Netherlands [22] Filed: Sept. 21, 1971 [21] Appl. No.: 182,379

[30] Foreign Application Priority Data [58] Field of Search.....3 13/278, 341, 346 R, 346 DC Primary Examiner-David Schonberg Assistant Examiner-Paul A. Sacher Attorney-Frank R. Trifari 5 7] ABSTRACT A directly heated cathode assembly comprising a tapeshaped member having a perforated central plane portion and end portions longitudinally extending from two sides of the central portion, a cathode plate member in spaced confronting relationship with one surface of the central portion, and electron emissive material embedded within the perforations of the central portion and interposed between the cathode plate member and the central portion. The width of the central portion of the tape-shaped member is greater than that of the end portions. The cathode plate member is [56] References Cited secured to the central portion of the tape-shaped UNITED STATES PATENTS member at two oppositely located positions of the central portion spaced from the end portions. 3,441,767 4/1969 Kerstetter ..3l3/341 X 8 Claims, 8 Drawing Figures 10 10 l Kli l l l PATENTEDSEPZs 1912 SHEET 2 [IF 3 INVENTOR$ ADRIANUS KUIPER JAN W. BROUNS BAUKE VISSER BY I lwhpeg /e.

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iwwa/e DIRECTLY HEATED OXIDE QATHGDE The invention relates to a directly heated oxide cathode, in particular a cathode having small dimensions and a short heating time, consisting of a tape of a high-melting point metal, for example tungsten or molybdenum, which comprises a widened perforated central plane of increased electrical resistance on which an emissive cathode plate is provided and which is supported by the oppositely located tape-shaped parts. The tape-shaped parts also serve as current supply conductors. The tape-shaped parts and the widened central parts can preferably be obtained by punching from a strip.

Such cathodes are known from the US. Patent Nos. 3,440,474 and 3,441,767.

In this known construction the widened central part is angular so that it has a comparatively high resistance. In the aperture of the ring is provided a slightly larger emissive pill consisting of a usual oxide mixture. The narrow tape-shaped current supply conductors cause only a low heat dissipation while the thermal energy evolves mainly in the annular central part.

Although with such a tape-shaped, directly heated oxide cathode a short heating time of approximately 2 sec. can be obtained, this known construction has several drawbacks. Such an annular central part is mechanically weak so that the tensioning force for holding the tape taut is critical and has to be adjusted accurately which necessitates complicated connection members, while the assembly is difficult. Too large a tensioning force deforms the annular central part so that the cathode pill may work loose. In addition the emission current in the pill experiences comparatively high resistance since the pill which consists of emissive oxides contacts the metal of the ring with its outer edge only. Moreover, the punching of tape with such an annular central part is difficult as a result of the small width of the edge of the ring.

A very favorable directly heated, rapidly heating oxide cathode consisting of a tape-shaped member having a perforated widened central plane portion of increased electrical resistance which is provided with electron-emissive material is obtained, if, according to the invention, the widened central plane portion is perforated in the form of a sieve and is embedded in emissive material which is present on a cathode plate which is connected in a metallically electrically conductive manner to the widened central plane portion only in two oppositely located places, the connection line of which extends at right angles to the longitudinal direction of the tape-shaped member.

The widened central plane portion preferably comprises two lugs, which extend at right angles to the longitudinal axis of the tape-shaped member and which are welded to corresponding lugs of the cathode plate, said lugs being then bent through 180 and forced against the non-emissive side of the cathode plate. This side of the cathode plate is preferably blackened, for example, by previously dipping the cathode plate in a nickel suspension and sintering the nickel powder on said plate.

The tape-shaped member preferably consists of tungsten, the cathode plate of nickel.

In order that the invention may be readily carried into effect, it will now be described in greater detail, by

way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a sectional view taken along the longitudinal axis of a cathode according to the invention, while FIG. 2 is a plan view, and

FIG. 3 is a side elevation;

FIG. 4 is a plan view of a cathode plate after punching, and

FIG. 5 is a side elevation of said plate after bending the connection lugs;

FIG. 6 is a plan view of the tape-shaped member after providing the perforation in the widened central plane, and

FIGS. 7 and 8 show a device for pressing the cathode plate on the widened central plane portion of the tapeshaped body and for welding the connection lugs.

Referring now to the figures, reference numeral 1 denotes a tape-shaped member which is punched from a tungsten plate, thickness from 15 to 20 11.. This member I has a widened central plane portion 2 which is perforated in the form of meshes or a sieve by a photographic etching method. This central plane portion has a diameter of 1 mm. The holes of the perforation have a diameter, for example, of 50 p. and a central distance of 60 p.. The light permeability of the plane 2 is 50 percent. The tape-shaped ends 3 of the member I serve as connection strips and as current supply members. The tape-shaped member 1 also serves as a filament. The resistance of the perforated central plane portion 2 being high, most of the thermal energy will be evolved here. In order to reduce the heat dissipation from the plane portion 2 to the connection strips 3 and the suspension members to which said strips are secured, elongate apertures 10 may be etched in the strips 3.

A nickel cathode plate 5 is secured to the sieve-like central plane portion 2 by means of two connection lugs 6. The plate 5 which is punched from a nickel plate having a thickness of 50 p. is first covered, by dipping in a nickel suspension, with a black nickel powder layer 8 which is sintered to the plate 5. The lugs 6 are then bent through (FIG. 5) and the surface of the cathode plate 5 remote from the lugs 6 is covered with a first emissive layer 7' which may be p. thick. This layer may consist of the usual carbonate mixture of barium, strontium and calcium and is provided across the black layer 8. The cathode plate 5 is then layed with the emissive layer 7 on the perforated central plane portion 2 of the tape-shaped member 1 and pressed with a die 11 (FIGS. 7 and 8). The pressure may be 200 g. The lugs 4 of the tape-shaped member 1 are then bent upwards across the lugs 6 and welded to said lugs 6 at 9. Since the line joining the welding points 9 is at right angles to the longitudinal axis of the tape-shaped member ll, 2, 3, they will have equal potentials. Since the cathode plate 5 is separated from the central plane portion 2 by the first emissive layer 7 which has a comparatively high resistance, said sieve-like central plane 6 is not shortcircuited by the plate 5.

The welded lugs 4, 6 are then bent and pressed until they engage the black surface of the plate 5 after which a second emissive layer 7 60 p. thick, is provided on the surface of the widened central plane portion 2 remote from the plate 5.

The sieve-like central plane portion is thus fully embedded in emissive material so that the resistance for the emission current is very low. Moreover there is no danger of the layer working loose or crumbling away.

The cathode described has a very short heating time since the heat dissipation along the lugs 3 is low, while the heating energy may be proportionally high as a result of the large thermal radiation of the black layer 8. Since said radiation plays a part only at high temperatures of the cathode, said heating energy at low temperature at which theradiation is still minimum, is in favor of the heating of the cathode. The operating temperature can thus be reached in a few seconds while the cathode forms a comparatively rigid assembly in that the material of the tape-shaped member need not also serve as a base for the emissive material and can consequently consist of a high-melting point metal, for example tungsten. The cathode plate 5 serves as a support for the emissive layer and therefore preferably consists of cathode nickel. This plate together with the emissive layers 7 and 7' in addition provides a larger rigidity to the sieve-like central plane portion 2 so that the tensioning force for holding the tape-shaped member 1,2,3 taut is not critical.

It is obvious that the shape of the widened central plane portion may be chosen arbitrarily, for example be square or oval.

What is claimed is:

1. A directly heated cathode assembly comprising a tape-shaped member having a central plane portion and end terminal portions longitudinally extending from two sides of said central portion, said central portion having a width greater than said end portions and being provided with a plurality of perforations, a

cathode plate member in spaced confronting relationship with one surface of said central portion, electron emissive material embedded within said central portion and interposed between said cathode plate member and said central portion, and means for securing said cathode plate member to said central portion at two oppositely located positions of said central portion spaced from said end portions.

2. A directly heated cathode assembly as claimed in claim 1, wherein said tape-shaped member essentially consists of a metal having a high melting point.

3. A directly heated cathode assembly as claimed in claim 1, wherein said tape-shaped member essentially consists of tungsten.

4. A directly heated cathode assembly as claimed in claim 1, wherein said tape-shaped member essentially consists of molybdenum.

5. A directly heated cathode assembly as claimed in claim 1, wherein said cathode plate member essentially consists of nickel.

6. A directly heated cathode assembly as claimed in claim 1, further comprising a layer of black nickel powder sintered to the surfaces of said cathode plate member.

7. A directly heated cathode assembly as claimed in claim 1, further comprising mating welded lugs on said tape-shaped member and said cathode plate member, said lugs being bent and pressed against the surface of said cathode plate member remote from the emissive surface.

8. A directly heated cathode assembly as claimed m claim 1, wherein said tape-shaped member comprises end portions having elongated apertures. 

1. A directly heated cathode assembly comprising a tape-shaped member having a central plane portion and end terminal portions longitudinally extending from two sides of said central portion, said central portion having a width greater than said end portions and being provided with a plurality of perforations, a cathode plate member in spaced confronting relationship with one surface of said central portion, electron emissive material embedded within said central portion and interposed between said cathode plate member and said central portion, and means for securing said cathode plate member to said central portion at two oppositely located positions of said central portion spaced from said end portions.
 2. A directly heated cathode assembly as claimed in claim 1, wherein said tape-shaped member essentially consists of a metal having a high melting point.
 3. A directly heated cathode assembly as claimed in claim 1, wherein said tape-shaped member essentially consists of tungsten.
 4. A directly heated cathode assembly as claimed in claim 1, wherein said tape-shaped member essentially consists of molybdenum.
 5. A directly heated cathode assembly as claimed in claim 1, wherein said cathode plate member essentially consists of nickel.
 6. A directly heated cathode assembly as claimed in claim 1, further comprising a layer of black nickel powder sintered to the surfaces of said cathode plate member.
 7. A directly heated cathode assembly as claimed in claim 1, further comprising mating welded lugs on said tape-shaped member and said cathode plate member, said lugs being bent 180* and pressed against the surface of said cathode plate member remote from the emissive surface.
 8. A directly heated cathode assembly as claimed in claim 1, wherein said tape-shaped member comprises end portions having elongated apertures. 